It isn’t a question of whether of not you are turned on by your woman or what she does but instead it is what you are doing yourself that diminishes the urgency of your sex drive that leaves you with low motivation. This is wholly your own fault not hers, unless it is that she is a complete turn off than I would wonder why you got involved with her in the first place.
No, it is your own fault and what ever you are doing on the side or in-between your intimate sessions with her is what is diminishing your sex drive. Yes, you can alter this with pills but that is only a temporary solution and in the long run once your system builds up a resistance to the pills you are going to be right back where you started from and you won’t be able to correct it from there. So blaming her won’t help. Neither would be going to a public place and engaging in sexual play on the sly. Like drugs you will keep seeking greater and greater thrills just to get you off but your system will only respond up to a point and taking it to the next level only increases the risk of running afoul of indecent behavior. So too porn is similar in that it will only stimulate to a point then you must seek greater thrills or it’s effectiveness will slowly slip away.
The solution is simple, if the food you are eating has lost its savor you simply stop eating until you are hungry again (this also works for dieting). So stop doing what you are doing on the side and wait until you are driven to the point where you can not think straight, than you will find that no matter what she does you will still find that release.
Another thing that helps is making your fantasies more realistic. This helps on two levels. One, living your fantasy only increases the value of your relationship and second this kind of fantasy can’t haunt you later.